Forces (F)Forces (F)DefinitionDefinition: a push or pull that has the : a push or pull that has the ability to cause a change in motionability to cause a change in motionStandard unit is the Standard unit is the NewtonNewton

Where did this unit Where did this unit come from??come from??

Sir Isaac NewtonSir Isaac Newton English physicist and English physicist and

mathematicianmathematician Laws of Motion and Laws of Motion and

GravitationGravitation Invented CalculusInvented Calculus

All before the age All before the age of 30!of 30!

Types of ForcesTypes of ForcesForces cause Forces cause motionmotionMotion depends on Motion depends on net net forceforce

NET means “total” or “sum”Forces can beForces can be balancedbalanced oror unbalancedunbalanced

Balanced ForcesBalanced Forces

Like a tie in Like a tie in an arm an arm wrestling wrestling match!match!

EqualEqual in size in sizeOpposite in Opposite in directiondirectionNo motionNo motion occurs! occurs! (equilibrium(equilibrium))

p. 51p. 51

Unbalanced ForcesUnbalanced Forces

Can be in the same direction OR in opposite directionsForces must be unbalanced to cause a change in motion

Unequal in size

As a box is sliding down a ramp, a 10 N force of gravity is pulling the

box down the ramp while a 2 N force of friction acts to stop the

box. What is the What is the net (total) net (total)

force force accelerating accelerating

the boxthe boxdown the down the ramp? ramp?

(Magnitude (Magnitude and and

Direction!!)Direction!!)

8 N to the 8 N to the RightRight

1 N 3 N

1 N 1N

1 N 1N

FFnetnet = 1N – 3 N = 1N – 3 N

= -2N= -2NFFnetnet = 1N +1 N = 1N +1 N

= +2N= +2NFFnetnet = -1N – 1 N = -1N – 1 N

= -2N= -2N

What is the Net What is the Net Force???Force???

FrictionFrictiona force that goes a force that goes againstagainst

motionmotion

1. Air friction (Resistance)2. Viscous friction 3. Sliding friction4. Rolling friction

Four Types of Friction:Four Types of Friction:

Also calledAlso called Air resistanceAir resistance (aerodynamics reduce (aerodynamics reduce

the air friction the air friction))

1. Air Friction1. Air Friction

Ex - falling objects or airplanes

Moving Moving through a through a liquid, or fluidliquid, or fluid

2. Viscous Friction2. Viscous Friction

Ex. - swimming

3. Sliding Friction3. Sliding FrictionTwo surfaces rub Two surfaces rub

against one against one anotheranotherEx - rubbing hands or

clapping

Oil and other lubricants help Oil and other lubricants help reduce friction.reduce friction.

An object An object rolls rolls over a over a surfacesurface

4. Rolling Friction4. Rolling Friction

Ex – any object with wheels

A_World_Without_Friction.asf

Gravity causes all falling Gravity causes all falling objects to accelerate at objects to accelerate at

the same rate.the same rate. (9.8 m/s(9.8 m/s22))

GravityGravityDefDef. - A downward force that causes objects to accelerate to the center of mass

Free Fall Tower GizmoFree Fall Tower Gizmo

Apollo 15 HammeApollo 15 Hammer and Feather Dror and Feather Dropp

MythbustersMythbusters Recreates Apollo Recreates Apollo 15 Drop15 Drop

MassMassAmount of matter Amount of matter inside of an objectinside of an object

Is NOTIs NOT

WeightWeightA measure of the A measure of the

forceforce created as your created as your mass responds to mass responds to

gravitygravity

(g(g))

(N)(N)

Formula:Formula:

FFww== mmggForce Force

of of Weight Weight

(N)(N)

Mass Mass (Kg)(Kg)

Gravity = Gravity = 9.8 m/s9.8 m/s22

p. 53p. 53

Calculating WeightCalculating Weight

Let’s look at how Let’s look at how massmass, , weightweight, and , and gravitygravity are are

related. related.

MassMass DOES NOTDOES NOT changechange,, but your but your weightweight will will change if there is a change if there is a change in change in gravitygravity

What would What would happen to happen to your your weightweight if if you were on you were on the Moon? the Moon?

What would What would happen to happen to your your massmass if if you were on you were on the Moon?the Moon?

Weight and Mass GizmoWeight and Mass Gizmo

Law of Universal Gravitation

Newton said that gravitational force depends on 2 things2 things:The DISTANCEDISTANCE from the center

of gravityThe MASSMASS of the objects

LESS gravitational force

MORE gravitational force

The yellowyellow objectobject has more gravitational force than the red objectred object because the yellow objectyellow object has more MASSMASS.

The mass of the

moon is much

smaller than the mass of

the Earth, so the

Moon is controlled

by the gravitational pull of the Earth.

The pull of gravity also

keeps satellites orbiting around

the Earth

Does the moon’s gravitational pull effect the Does the moon’s gravitational pull effect the Earth? Earth? Yes, the moon’s

gravity is large enough to actually pull water out of the ocean from space…

Well, not quite that

much...just enough to

create motion of the tides.

As you move further from the center of As you move further from the center of the Earth, the force of gravity the Earth, the force of gravity DECREASES.DECREASES.

Where would you weigh less, in Where would you weigh less, in Galveston or in Denver?Galveston or in Denver?

Denver is the “Mile High City”; the Denver is the “Mile High City”; the force of gravity is less. Therefore, force of gravity is less. Therefore, the force of gravity would be less the force of gravity would be less because it is further away from the because it is further away from the center of the Earth, and you would center of the Earth, and you would weigh weigh slightly slightly less.less.

Gravity Song!

Newton’s First Law (Law of Newton’s First Law (Law of Inertia) Inertia) An object at rest stays at An object at rest stays at

rest and an object in motion rest and an object in motion keeps its same motion, keeps its same motion, UNLESS an UNLESS an outsideoutside force force acts on it. acts on it.

Teenage TermsTeenage Terms – Objects will keep – Objects will keep doing what they are doing unless doing what they are doing unless an outside force changes that!an outside force changes that!

InertiaInertiaDefDef. - The tendency of . - The tendency of an object to resist any an object to resist any change in motion change in motion

You must overcome inertia You must overcome inertia to start or stop motionto start or stop motion

Depends on the Depends on the mass mass of of the objectthe object

AsAs mass , inertia willmass , inertia will

Which object has Which object has the greatest amount the greatest amount

of INERTIA??of INERTIA??PencilPencilBaseballBaseballBowling BallBowling BallPing Pong BallPing Pong Ball

INERTIAINERTIA is what causes a person (or is what causes a person (or anything else in the) involved in a anything else in the) involved in a head-on collision to continue moving head-on collision to continue moving forward at the forward at the samesame speed that the speed that the car was traveling, until some outside car was traveling, until some outside force causes it to stop force causes it to stop (i.e.- seatbelt, (i.e.- seatbelt, windshield, etc.)windshield, etc.)

What’s wrong with this What’s wrong with this picture??picture??

InertiaInertia

Other Examples of 1Other Examples of 1stst LawLaw

Card TricksCard TricksDishes and table clothDishes and table clothCollisions and Collisions and seatbeltsseatbeltsCrash Test DummiesCrash Test Dummies

Bike Ramp CrashBike Ramp CrashFirst Law, Inertia, and First Law, Inertia, and Friction VideoFriction Video

containedhttp://wwwghttp://www

Newton’s 2Newton’s 2ndnd Law (F = Law (F = ma)ma)

The acceleration of an object is The acceleration of an object is directlydirectly proportionalproportional to the to the forceforce acting on it and acting on it and inverselyinversely proportionalproportional to its to its massmass..

F, a (direct relationship)F, a (direct relationship)

m, a (inverse relationship)m, a (inverse relationship)

Force and Acceleration areForce and Acceleration are Directly ProportionalDirectly Proportional

F aF a 2 N 2 N

4 N

F=ma 2N =(1kg)a

a= 2 m/s2

F=ma 4N =(1kg)a

a= 4 m/s2

Mass and Acceleration areMass and Acceleration are Inversely ProportionalInversely Proportional

m, a (inverse m, a (inverse relationship)relationship)

F = ma 1 N = (1kg) a a = 1m/s2 F= ma 1 N =

(2kg) a a = 0.5 m/s2

Solving 2Solving 2ndnd Law Problems Law Problems

Use the formula:Use the formula:

Unit for Force is Unit for Force is Newtons (N)Newtons (N)

Unit for Unit for Mass is Mass is

kilograms kilograms (kg)(kg)

Unit for Acceleration

is m/s2

Solving 2Solving 2ndnd Law Problems Law Problems

What force is required to give What force is required to give a 5 kg box an acceleration of a 5 kg box an acceleration of 2 m/s2 m/s2 2 ??

Variables Formula Plug-n chug Variables Formula Plug-n chug Answer Answer

F= ? F= ?

m=5 kg m=5 kg

a= 2m/sa= 2m/s22

Solving 2Solving 2ndnd Law Problems Law Problems

What force is required to give What force is required to give a 5 kg box an acceleration of a 5 kg box an acceleration of 2 m/s2 m/s2 2 ??

Variables Formula Plug-n chug Variables Formula Plug-n chug Answer Answer

F= ? F = ma F= ? F = ma

m=5 kg m=5 kg

a= 2m/sa= 2m/s22

Solving 2Solving 2ndnd Law Problems Law Problems

What force is required to give a 5 What force is required to give a 5 kg box an acceleration of 2 kg box an acceleration of 2 m/sm/s2 2 ??

Variables Formula Plug-n chug Variables Formula Plug-n chug AnswerAnswer

F= ? F = ma F =(5kg)(2m/sF= ? F = ma F =(5kg)(2m/s22))

m=5 kg m=5 kg

a= 2m/sa= 2m/s22

Solving 2Solving 2ndnd Law Problems Law Problems

What force is required to give a 5 What force is required to give a 5 kg box an acceleration of 2 kg box an acceleration of 2 m/sm/s2 2 ??

Variables Formula Plug-n chug Variables Formula Plug-n chug AnswerAnswer

F= ? F = ma F =(5kg)(2m/sF= ? F = ma F =(5kg)(2m/s22))

m=5 kg m=5 kg

a= 2m/sa= 2m/s22 F= F= 10N10N

Solving 2Solving 2ndnd Law Problems Law Problems

Explains why you can throw a Explains why you can throw a baseball further than a baseball further than a bowling ballbowling ball

Braking force required to Braking force required to stop a Volkswagen vs. a dump stop a Volkswagen vs. a dump trucktruck

Why a Mustang accelerates Why a Mustang accelerates faster than a busfaster than a bus

1.1.What is the acceleration of a What is the acceleration of a 500 kg ball rolled with a force 500 kg ball rolled with a force of 3.6N?of 3.6N?

2.2.A rollercoaster accelerates at a A rollercoaster accelerates at a rate of 30 m/srate of 30 m/s22. If the . If the rollercoaster has a mass of rollercoaster has a mass of 10,345 kg, what size force must 10,345 kg, what size force must be applied?be applied?

3.3.What is the mass of a tanker What is the mass of a tanker truck that accelerates at 15 m/struck that accelerates at 15 m/s22 with a force of 2500 N?with a force of 2500 N?

Newton’s 3Newton’s 3rdrd Law Law (Action/Reaction)(Action/Reaction)

Whenever one object Whenever one object exerts a force on another exerts a force on another (action), the second object (action), the second object exerts an equal and exerts an equal and opposite force (reaction) opposite force (reaction) on the first.on the first.

All forces come in pairs.All forces come in pairs.

Newton’s Third Law: Newton’s Third Law: For every action there is an equal

and opposite reactionLook at the picture below:

What is the action?

What is the reaction?

The gases push downward out of the rocket

The the rocket is pushed upward by the gases

Examples of 3Examples of 3rdrd Law Law Leaning on wallLeaning on wall (action: you push on wall, (action: you push on wall,

reaction: wall pushes back on you)reaction: wall pushes back on you) Firing a cannonFiring a cannon (action: cannon pushes on (action: cannon pushes on

cannon ball, reaction: cannon ball pushes back cannon ball, reaction: cannon ball pushes back on cannon) on cannon)

WalkingWalking (action: you push on the earth, (action: you push on the earth, reaction: the earth pushes back on you)reaction: the earth pushes back on you)

Space Shuttle taking offSpace Shuttle taking off (action: rocket (action: rocket thrusters push down, reaction: the space shuttle thrusters push down, reaction: the space shuttle travels upward)travels upward)

America’s Funniest America’s Funniest VideosVideos

Dorm Chair Hit Dorm Chair Hit (Newton’s Third Law & (Newton’s Third Law & Conservation of Momentum)Conservation of Momentum)

http://http://abc.go.com/primetime/afv/indabc.go.com/primetime/afv/index?pnex?pn==videoplayer&idvideoplayer&id=363529=363529

An object will maintain a constant state of motion until acted upon by

an “unbalanced” force.This law shows how force, mass and

acceleration are related. Force = mass x acceleration

For every action there is an equal and opposite reaction

Formula:Formula:

pp== mmvvMomentum Momentum

(Kg-m/s)(Kg-m/s)

Mass Mass (Kg)(Kg)

Velocity Velocity (m/s)(m/s)

Calculating Calculating MomentumMomentum

•UnitUnit: kg m/s: kg m/s

Will two moving Will two moving objects with the objects with the same mass always same mass always have the same have the same momentum??momentum??

MASS = 100

kg

(About 220 lbs)

V = 1 V = 1 m/sm/s

V = 3 m/sV = 3 m/s

NO!! Their NO!! Their velocities need to velocities need to be considered!!be considered!!

3 Examples of Mo3 Examples of Momentummentum

Momentum of a MaMomentum of a Marble in a Bowlrble in a Bowl

Total amount of Total amount of momentum can not changemomentum can not change

Law of Conservation of Law of Conservation of MomentumMomentum

What is the momentum What is the momentum of a blackbird with a of a blackbird with a mass of 0.04 kg flying mass of 0.04 kg flying at 19 m/s?at 19 m/s?

A meteorite has a A meteorite has a momentum of 100 kg-m/s. If momentum of 100 kg-m/s. If the velocity is 1000 m/s, the velocity is 1000 m/s, what is its mass?what is its mass?

A frog with a mass of 0.9 kg A frog with a mass of 0.9 kg hops with a momentum of hops with a momentum of 10.8 kg-m/s. What is its 10.8 kg-m/s. What is its speed?speed?